Two boxes, both ways
Type in Plain text and the code appears on the right; paste a code into Code and the message appears on the left. Pick a different code and whatever you typed last is translated again, so one pasted code can be tried against all ten in a few clicks. The swap button moves the text across to the other box and translates it the other way, which is how you stack two codes.
Which code is it?
The look of a code usually gives it away. Only dots, dashes and slashes is Morse. Only 0s and 1s, often in groups of eight, is binary, and pairs of 0 to 9 and a to f are hex. Numbers from 1 to 26 joined by dashes are A1Z26. A run of letters, digits, + and / that often ends in = or == is Base64. Word-shaped groups of letters that read as nonsense are a letter swap: try ROT13 and Atbash first, as they need no setting, then Caesar with each shift, then Vigenère if you have a keyword.
Base64 and Reverse
Base64 packs the bytes of the text into letters, digits, + and /, using UTF-8 so accents and emoji survive; it is how email attachments and data links carry text, and aGk= is hi. Reverse writes the text backwards, character by character, so stressed becomes desserts. Both work in either box like the other codes.
Questions
Are these codes secure?
No. They are puzzles, not protection: every one of them can be cracked in seconds, often by hand. They are great for escape rooms, treasure hunts and notes in class. To keep something private, use Encrypt Text, which uses real AES-256 encryption with a password.
Why does the code box turn red?
What is in it cannot be read in the chosen code: a number over 26 in A1Z26, a pattern of dots and dashes that is not a letter in Morse, or characters that do not belong in binary, hex or Base64. That is a useful clue in itself: move on to the next code.
Is my message sent anywhere?
No. Everything is translated in this page on your device, and nothing is saved once you close it.